Implantable neurostimulation systems have proven therapeutic in a wide variety of diseases and disorders. For example, Spinal Cord Stimulation (SCS) techniques, which directly stimulate the spinal cord tissue of the patient, have long been accepted as a therapeutic modality for the treatment of chronic pain syndromes, and the application of spinal cord stimulation has expanded to additional applications, such as angina pectoralis, peripheral vascular disease, and incontinence, among others.
An implantable SCS system typically includes one or more electrode-carrying stimulation leads, which are implanted at a stimulation site in proximity to the spinal cord tissue of the patient, and a neurostimulator implanted remotely from the stimulation site, but coupled either directly to the stimulation lead(s) or indirectly to the stimulation lead(s) via a lead extension. The neurostimulation system may further comprise a handheld patient programmer to remotely instruct the neurostimulator to generate electrical stimulation pulses in accordance with selected stimulation parameters. The handheld programmer may, itself, be programmed by a technician attending the patient, for example, by using a Clinician's Programmer (CP), which typically includes a general purpose computer, such as a laptop, with a programming software package installed thereon.
Thus, programmed electrical pulses can be delivered from the neurostimulator to the stimulation lead(s) to stimulate or activate a volume of the spinal cord tissue. In particular, electrical stimulation energy conveyed to the electrodes creates an electrical field, which when strong enough, depolarizes (or “stimulates”) the neural fibers within the spinal cord beyond a threshold level, thereby inducing the firing of action potentials (APs) that propagate along the neural fibers to provide the desired efficacious therapy to the patient.
Spinal cord stimulation is an application of the “gate control theory,” which theorizes that painful stimuli can be modulated by touch and vibratory sensations. Nociceptive information (i.e., related to painful stimuli) is carried by small nerve fibers, while innocuous (e.g., touch, vibration, pressure) information is carried by large nerve fibers, both of which interact within the dorsal horn of the spinal cord (the ostensible location of the “the gate”). The gate control theory suggests that activation of large nerve fibers carrying touch and vibratory sensation may be manipulated to “close the gate” to the small nerve fibers carrying painful peripheral stimuli. As such, spinal cord stimulation acts as an analgesic, relieving pain by stimulating the branches of the large nerve fibers in the dorsal columns, which then deliver action potentials to the dorsal horn, thereby counteracting the painful stimuli carried by corresponding small nerve fibers. In order for spinal cord stimulation to function effectively, the stimulation must be applied to the appropriate large nerve fibers that correspond to the small nerve fibers carrying the painful stimuli. That is, the applied stimulation must be carefully mapped to the painful body area. Programming and mapping procedures have been developed in order to ensure that the appropriate large nerve fibers are stimulated during SCS to provide effective treatment of pain.
Discogenic back pain is believed to be nociceptive in nature. With intervertebral disc degeneration, increased nerve fiber growth into the outer annulus of the intervertebral disc is observed, and these fibers can become sensitized and thus hyperactive. These nerve fibers are believed to be pain-carrying afferents traveling within the sinuvertebral nerves, which run within or around the posterior longitudinal ligament of the spine near the affected levels of the degenerating discs. SCS has been shown to provide some pain relief in patients with discogenic pain, though the exact mechanism of relief is not known.
However, while SCS techniques may blunt the pain, they typically do not block the pain sensation altogether. There, thus, remains a need for a SCS technique that provides direct inhibition of the pain signals from the degenerated intervertebral discs.